Dynamic Response of Existing R.C. Bridges Against Earthquake Forces

Abstract

Performance of bridges against earthquake forces is different from buildings and other kind of structures as bridges are long and narrow, and support fleeting populace on highways or railways. Earthquakes with magnitude greater than 6.0 are capable of damaging or sometimes leading to even collapse of lifeline bridges, resulting in human and socio-economic losses. The extent of earthquake damage depends on the location of bridge close to the nearest seismic zone, structural configuration, ductility demand, age, and characteristics of the soil below foundation. Many failure examples during recent past earthquakes demand the scientific community and civil engineers, the importance of designing bridge structures against seismic forces; particularly when they built on loose soils. Vertical and lateral loads are resisted by the frame action of the superstructure and substructure of the bridge. Abutments and piers or supporting columns resist lateral forces in proportion to their relative stiffness. The vulnerability of any bridge during an earthquake is mainly due to the lateral displacements which cause large shear and flexure in pier or abutment and lead to failure at connections between the pier top and superstructure, or pier bottom and foundation. In the present study, an example of a two-lane and four spanned R.C. T-beam bridge across a canal, located in seismic zone III, is chosen for carrying out dynamic analysis against seismic forces and checked whether the bearing seat width provided at top of abutment and pier is safe or not, against the horizontal displacement of abutment and pier, obtained from the analysis due to seismic forces.